<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=u, initial-scale=1.0">
    <title>Document</title>
    <style>
        ul {
            position: relative;
            width: 200px;
        }
        li {
            list-style: none;
            width: 200px;
        }
        li:hover .tab{
           height: 60px;
           opacity: 1;
        }
        .tab {
            margin-left: 20px;
            position: absolute;
            right: -15px;
            top: 0;
            opacity: 0;
            width: 200px;
            height: 0;
            transition: all 0.3s 0.1s;
            background-color: pink;

        }
    </style>
</head>
<body>
    <ul>
        <li>
            <span>1</span>
            <div class="tab">11</div>
        </li>
        <li>
            <span>2</span>
            <div class="tab">22</div>
        </li>
        <li>
            <span>3</span>
            <div class="tab">33</div>
        </li>
    </ul>
</body>
</html>